Just to be crystal clear about the method so far:
right click The Stanley Parable app and click "show package contents"
go to Contents/MacOS/run.sh
open this in a text editor
find the line of code that says "#location of the binary" and replace the line below with
GAMEROOT="$HOME/Library/Application Support/Steam/SteamApps/common/Half-life 2"
aquantumsingularity
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